Power over Ethernet (PoE), in accordance with both IEEE 802.3af-2003 and IEEE 802.3at-2009, each published by the Institute of Electrical and Electronics Engineers, Inc., New York, the entire contents of which is incorporated herein by reference, defines delivery of power over a set of 2 twisted wire pairs without disturbing data communication. The aforementioned standards particularly provides for a power sourcing equipment (PSE) and a powered device (PD). The power sourcing equipment is configured to detect the PD by ascertaining a valid signature resistance, and supply power over the 2 twisted wire pairs only after a valid signature resistance is actually detected.
Detection, in accordance with either of the above standards requires the supply of at least 2 voltage levels between the range of 2.8 volts and 10 volts, with a signature resistance of the PD determined based on a calculation of the actual voltage levels, or current, detected. The use of 2 voltage levels allows for determination of the signature resistance irrespective of the existence of a diode bridge, typically supplied at the input to the PD.
U.S. Pat. No. 7,849,343 issued Dec. 7, 2010 to Ferentz et al, the entire contents of which is incorporated herein by reference, is addressed to a method and apparatus for preventing harmful transients resulting from a probing routine for a valid PD 180 detection signature in a network. The method comprises providing a pre-detection output voltage via an impedance; obtaining an indication of the pre-detection output voltage; comparing the indication of the pre-detection output voltage with a pre-determined value; and in the event that the indication of the pre-detection output voltage is less than the pre-determined value; initiating a probing routine for a valid powered device detection signature.
European Commission Regulation (EC) No 278/2009 directs that ecodesign requirements for no-load condition electric power consumption of external power supplies shall not exceed 0.50 Watts one year after the regulation has come into force. Additionally, the regulation directs that two years after the regulation has come into force the no-load condition electric power consumption is not to exceed 0.30 Watts for power supplies delivering less than 51 Watts when active.
What is desired is a PSE architecture capable of meeting such inactive state energy draw requirements.